Rb20det compression test ??

[mgp87zxt]

what numbers would a perfect factory rb20det produce?

Im looking at a clip with:

1. Cylinder # 1 1252. Cylinder # 2 1303. Cylinder # 3 1254. Cylinder # 4 1355. Cylinder # 5 1256. Cylinder # 6 135

motor supposidly has 83000 kilometers on it. But its in australia so who knows how much use its got on it.

[Yellow4g63]

THose #'s look really low. if it's 8.5:1 then it should be around 160ish. Try to put a cap full of oil in each of cylinders and crank it with the throttle open and see if the #'s change.

[wcbjr]

At least they are all similar.

[PROJECTRB240SX]

ITS 150 IS MINIMUM BY MY ESM AND 165 IS PERFECT.

[JeffTN]

Do a cylinder leakage test too. That might reveal some stuff.

[PROJECTRB240SX]

A LEAK-DOWN TEST IS ONLY EFFECTIVE IF HE SMELLS FUEL IN THE OIL.

[JeffTN]

What? You lost me. A leak down test will tell you if you are losing compression through the valves or rings.

Am I reading this wrong...here. It does not say anything about fuel.

[wcbjr]

I've never seen all 6 run equally low. Seems like the method or gauge is wrong.

[PROJECTRB240SX]

SO WHAT LEAK TEST ARE YOU REFFERING TO?

[wga240]

Did you make sure to press the throttle all the way down when doing the test? If you don't, you'll get low numbers.

[JeffTN]

Read that link I posted. ^^^ Its pretty informative.

[PROJECTRB240SX]

THERE WOULD BE THE SMELL OF FUEL IN THE OIL IF THE RINGS WERE GOING BAD, IF THE VALVES WERE GOING BAD THE HEAD WOULD GET REALLY HOT.

[PROJECTRB240SX]

THATS THE TEST BUT IF THE RINGS WERE LEAKING THE FUEL WOULD BE GETTTING INTO THE OIL, HENCE THE SMELL OF FUEL IN THE OIL.

[kevy8up]

would it be wise to do a rings and seals rebuild when u get the engine in. Since one would have it out and eventually swap it.

[JeffTN]

That is way beyond me cause I have never heard that before. How is losing compression and the smell of fuel related. Do you have a link to something that I can read about this?

[JeffTN]

would it be wise to do a rings and seals rebuild when u get the engine in. Since one would have it out and eventually swap it.

If it aint broke, dont fix it. I would make sure that it is broke before I just tore into it. When you start doing this rings and stuff, then you should replace the rod and main bearings too. You can do a leak down test while its out to determine if it does infact leak comperssion.

[PROJECTRB240SX]

Ok the rings are there to keep the oil and the fuel separated, if the ring goes bad they mix. sure signs are white/grey smoke from tailpipe and oil smelling of fuel. A leak down test tests how much of that stuff is separated 5% or less is optimal. Low compression is a side effect of this.

[Nameless EJ6]

I hope they heated the engine up to check before they did that compression test, otherwise it means basically nothing. Dry compression tests are really almost useless.

Anyways, some of you guys don't seem to understand what a compression test tells you. When you do a compression test, the BIG thing you are looking for is variation between cylinders. Low numbers mean NOTHING unless they are extremely low. Your numbers are fairly even across all cylinders, so I wouldn't even worry about this ****. I have seen even lower numbers on other turbo engines that ran perfect.

Rings are there for two main reasons. To "scrape" the cylinder walls of oil and to provide a seal with the help of combustion pressures. That's just good to know when you're doing this stuff. Rarely does raw fuel contaminate the oil by seeping past the rings. It is usually blow by gasses after combustion escaping past the rings that contaminate oil. Smelling fuel in the oil doesn't mean anything when it comes to compression or leak down, because the engine may also have poor crank case ventilation. And all engines have seepage past the rings. So lets please forget that method.

Like said before, a leak down test is the best way of diagnosing sealing problems.

If I was you, I'd get the engine running before you make any real diagnosis. The compression looks fine.

[FAST-DATSUN]

Nameless is right a cold compression test is only a ball part ##. you need the engine up to operating temp the do the test. remove all the plugs, disable the ignition, crank each cylinder your testing 5-6 times for the test and all cylinders the SAME. A leakdown test is more accuarte...meaure of the engine condition and what is good or bad..

[crxcess]

i just did a compression test on my rb20 and it read 145 all the way across.

[Joe]

A LEAK-DOWN TEST IS ONLY EFFECTIVE IF HE SMELLS FUEL IN THE OIL.

what?

a CLT is the best test of all time

you can see if you are losing compression from valves, rings, or headgasket.

and the numbers are low but they are low TOGETHER. i have a feeling they didnt do the test correctly.

if 1 cylinder was like 15lbs lower than the other i would worry.

make sure they do it properly, remove all spark plugs and WOT.

[crxcess]

Thats what I did...the car was warm too. Brand new tester.

[Nameless EJ6]

Thats what I did...the car was warm too. Brand new tester.

145 across is perfectly fine for a low compression motor such as the RB20. The turbo is what makes the real compression on a FI motor.

My ol JDM ITR engine hit 225 across all cylinders with 11:1 compression. That thing screamed harder than any other stock ITR engine I've seen - yet stupid people always seem to tell me the compression was low. I just Ignore that s***.

IMO, a compression test these days should only be used if there is reason to think there is internal damage - like a slightly bent rod or a damaged valve. You want real diagnosis, go straight to the leak down.